1. Field of the Invention
The present invention relates to ultrasound transducers devices for the destruction of adipose tissue through the projection of ultrasound energy into adipose tissue without an invasive component. In particular this invention details transducers having multiple focal points, or devices using multiple transducers to perform non-invasive adipose tissue destruction.
2. Description of the Prior Art
Body sculpting has developed into a highly sought after procedure for reducing a person's weight and restoring people to a leaner, trimmer physique. The field of cosmetic surgery has ballooned considerably with developments in both tools and techniques. One of the more popular for both quick weight loss and body sculpting is liposuction.
Liposuction is a method of body contouring that can dramatically improve the shape and contour of different body areas by sculpting and removing unwanted fat. More than 200,000 liposuction procedures are performed annually. Recent innovations and advances in the field of liposuction include the tumescent technique and an ultrasonic assisted technique. Traditional liposuction was done by making small incisions in desired locations, then inserting a hollow tube or cannula under the skin in the fat layer. The cannula is connected to a vacuum and the fat is vacuumed out under high suction pressure. This procedure indiscriminately removed fat, connective tissue, blood vessels and nerve tissue. The procedure caused bleeding, bruising, trauma, and blood loss, restricting the amount of fat removal possible.
The Tumescent technique allows for removal of significantly more fat during the operation with less blood loss. Tumescent liposuction injects a fat layer with large amounts of saline and adrenalin solution before suctioning. A cannula is again used with a suction device to remove fat. This procedure reduces the bleeding of traditional liposuction. However the procedure still removes a significant amount of structural tissue, blood and nerve endings.
The most recently approved innovation is Ultrasound Assisted Lipoplasty (UAL). UAL utilizes a titanium cannula that has the tip vibrating at ultrasound frequency. This vibration disrupts the near volume fat cells and essentially liquefies them for easy removal. UAL uses a low power suction and draws the fat material only in the near vicinity of the cannula tip. This technique is more refined and gentle to the tissues, there is less blood loss, less bruising, less pain, and a significantly faster recovery.
The use of ultrasound for surgical procedure is not restricted to UAL. High intensity focused ultrasound (HIFU) techniques have been employed by others for cancer therapy.
U.S. Pat. No. 6,309,355 to Cain et al., discloses a method of generating micro-bubbles in a target tissue and then using an ultrasound source to cause the micro bubbles to create a cavitation effect to destroy nearby tissue. The preferred embodiment utilizes a low frequency ultrasound source (less than 500 kHz) to cause the cavitation. A diagnostic instrument is used to determine the location of the individual surgical lesions.
PCT application WO 02/054018 A2 to Eshel, et al., provides for a method of lysing adipose tissue in a region of the human body while simultaneously not lysing non-adipose tissue. The method describes the use of HIFU in the body coupled to a diagnostic imaging system and a computer to track the areas being irradiated with HIFU energy.
The following additional references are relevant in the art: U.S. Pat. Nos. 5,769,790; 6,113,558; 5,827,204; 5,143,063; 5,219,401; 5,419,761; 5,618,275; 6,039,048; 6,425,867; 5,928,169; 6,387,380; 6,350,245; 6,241,753; 5,526,815; 6,071,239; 5,143,063; and WO 00/36982
Current methods for using High Intensity Focused Ultrasound (HIFU) to form lesions in biologic tissues via cavitation effects suffer from a variety of practical limitations. In order to reach the intensities necessary for cavitation, previous work has typically involved use of physically large (i.e. of diameters greater than 2 cm, typically in the range of 5 to 10 cm) focused transducers at relatively low (i.e. less than 1.5 MHz) frequencies and fairly high (i.e. greater than 50 Watts) output energy. Large transducers and high power levels are typically required at low frequencies in order to reach local intensities at the transducer focal point of a magnitude sufficient for cavitation. Low frequencies, even approaching sonic frequencies (i.e. 20 KHz) may be preferred for cavitation effects. A physically large transducer practically limits clinical applications for several reasons.
Physical contact must typically be maintained between the entire active surface of a large transducer and a patient. This contact is often maintained through a coupling material in order to properly transmit the ultrasound energy into the target tissue. Larger transducers are more difficult to keep properly coupled due to natural contours of tissue. Ideally, there should be no intervening media between the transducer and the focal volume where the lesion is to be formed that pose large discontinuities in acoustic properties (thus causing reflections, refraction, and the like). Larger transducers are more difficult to position so that the entire aperture is clear of intervening media such as bone or gas pockets that may degrade or destroy the ability to focus properly. Furthermore, large transducers with very shallow focal depths are difficult, if not impossible to manufacture and apply properly. Typical ratios of focal depth to aperture size are not less than 1 (an f/1 design). Even if this ratio can be physically decreased, acoustic coupling becomes problematic due to critical angle effects. A standoff can be used to physically move the transducer away from the target tissue while maintaining coupling, but this has drawbacks in terms of increased intensity at the tissue surface, and simply being physically unwieldy.
In addition, the focal point of each transducer is at a fixed depth below the skin surface and the destruction of adipose tissue using a fixed focal length transducer cannot be adjusted by a user. Transducers are manufactured with specific frequencies, amplitudes, focal depths and power capabilities and these variables cannot be altered after the manufacturing process is complete. The result is that procedures which attempt to utilize high intensity focused ultrasound to produce adipose tissue destruction through heating, cavitation or some combination of the two, are restricted to operate at a particular tissue depth, and are unable to make even slight adjustments to the transducer parameters except to completely change transducers. Thus if a patient wishes to have a volume of adipose tissue treated that is large, such that a liposuction procedure would normally be called for, a high intensity focused ultrasound device would not be able to handle the depths and breadths as variables to the operation. Thus high intensity focused ultrasound procedure is still not a better option for the patient since the result is restricted to a thin layer of adipose tissue at a fixed depth below the surface of the skin.
Although liposuction procedures have been refined, and non invasive techniques and devices are in development, there is still a need for an ultrasound transducer that can produce the desired lesion formation to maximize effective lipolysis treatment in a short exposure time.
There is further a need for a transducer having an adaptive ability to conform to different procedural requirements involving changes in frequency, power output, and activation time.
There is still further a need for a transducer device capable of delivering high intensity focused ultrasound to a patient without causing producing skin burns.